The present invention relates, in general, to the field of circulating fluidized bed (CFB) boilers and, in particular, to improved impact type particle separator constructions comprised of fluid-cooled tubes.
CFB boiler systems are known and used in the production of steam for industrial processes and/or electric power generation. See, for example, U.S. Pat. Nos. 5,799,593, 4,992,085, and 4,891,052 to Belin et al.; 5,809,940 to James et al.; 5,378,253 and 5,435,820 to Daum et al.; and 5,343,830 to Alexander et al. In CFB reactors, reacting and non-reacting solids are entrained within the reactor enclosure by the upward gas flow which carries solids to the exit at the upper portion of the reactor where the solids are separated by impact type particle separators. The impact type particle separators are placed in staggered arrays to present a path which may be navigated by the gas stream, but not the entrained particles. The collected solids are returned to the bottom of the reactor. One CFB boiler arrangement uses a plurality of impact type particle separators (or concave impingement members or U-beams) at the furnace exit to separate particles from the flue gas. While these separators can have a variety of configurations, they are commonly referred to as U-beams because they most often have a U-shaped configuration in cross-section.
When applied to a CFB boiler, a plurality of such impact type particle separators are supported within the furnace enclosure and extend vertically in at least two rows across the furnace exit opening, with collected particles falling unobstructed and unchanneled underneath the collecting members along the rear enclosure wall. The gap between each adjacent pair of U-beams in one row is aligned with a U-beam in a preceding or following row of U-beams to present a tortuous path for the flue gas/solids to navigate. The U-beams in each row collect and remove particles from the flow of flue gas/solids, while the flue gas stream continues to flow around and through the U-beam array.
These types of collection elements are generally relatively long in comparison to their width and depth. The shape of the collection elements is usually dictated by two considerations: namely, the collection efficiency of the U-beams themselves and the ability of the U-beams to be self-supporting. When these elements are used, they are generally placed at the furnace exit and not cooled. Their placement at the furnace outlet is to protect the downstream heating surfaces from erosion by solid particles. Thus, the U-beams are exposed to the high temperatures of the flowing stream of flue gas/solids, and the materials used for the U-beams must be sufficiently temperature resistant to provide adequate support and resistance to damage.
Long, self-supporting stainless steel plate channels have been successfully used in CFB boilers for the primary solids collector, but the xe2x80x9ccreepxe2x80x9d strength of the commercially available and suitable alloys limits the length of the collection elements. By breaking up the long collection channel into short segments, the required strength of each short segment is much less than for the long channel due to the series of intermittent supports and the small amount of weight of any individual segment or element.
Methods of making collection elements which are cooled or supported off a cooled structure have usually included collection plates welded to water cooled support tubes. See U.S. Pat. Nos. 5,378,253 and 5,435,820 to Daum et al. However, welding to the cooling tubes increases the opportunity for tube leaks to occur at the welds.
In addition, under this known design structure, the collection element is cooled asymmetrically due to the proximity of the cooled tube or tubes to only some portion of the shaped collection channel segment or element. Thus, the plate forming the collection elements will tend to distort due to the differential expansion of the cooler areas in comparison to the hotter portions of the collection elements.
In addition, it is necessary to protect the tubes themselves from erosion caused by the impacting solids entrained within the solid/gas flow. This protection requires the use of tube shields made of stainless steel or ceramic which must be used along the entire height of the collector, which adds further cost.
The present invention comprises various arrangements of fluid-cooled tubes which are used to form impact type particle separators, commonly in a U-shape, but which can also be formed into W-, E-, V- or other shapes. Such impact type particle separators find particular use in circulating fluidized bed (CFB) boilers or reactors.
Accordingly, one aspect of the present invention is drawn to an apparatus for separating solids from flue gas in a circulating fluidized bed (CFB) boiler. In one embodiment, the apparatus comprises a plurality of vertical, impact type particle separators located within the CFB. The impact type particle separators are adjacently positioned and horizontally spaced from one another in a plurality of staggered rows. Each impact type particle separator includes a plurality of vertical cooling tubes for conveying a cooling medium therethrough. A plurality of slip fit elements having apertures which accept and surround the cooling tubes are provided, the plurality of slip fit elements cooperating with one another to form a collecting channel along a length of the cooling tubes formed by side walls and a back wall. The side walls and back wall have a plurality of separate vertically aligned segments extending longitudinally along the height of the impact type particle separator, each vertically aligned segment being connected at its ends to an adjacent segment.
Another aspect of the present invention is drawn to an apparatus for separating solids from flue gas in a circulating fluidized bed (CFB) boiler. In this embodiment, the apparatus comprises a plurality of vertical, impact type particle separators located within the CFB. The impact type particle separators are adjacently positioned and horizontally spaced from one another in at least two staggered rows. Each impact type particle separator includes a plurality of vertical cooling tubes for conveying a cooling medium therethrough. The plurality of cooling tubes forming an individual impact type particle separator are attached or connected to one another by intermediate tube alignment plate or bar welded at least intermittently inbetween and along the adjacent cooling tubes to form a unitary structure. A plurality of pin studs may be welded to the tubes, and then covered with a coating of refractory. Other erosion resistant mechanisms, such as tiles, metal or ceramic spray coatings, metal or ceramic castings, weld overlay, and shields, may be employed.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific benefits attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.